1. Field of the Invention
The present invention relates to a polyorganosiloxane catalyst, more specifically a polyorganosiloxane catalyst with both of a sulfonic acid group-containing hydrocarbon group and a mercapto group-containing hydrocarbon group. Such catalyst is used as the catalyst for producing bisphenol A by the dehydration-condensation of acetone and phenol.
2. Description of the Related Art
Bisphenol A [2,2-bis(4'-hydroxyphenyl)propane] is generally produced continuously in the mode of so-called flow reaction on fixed bed, comprising passing acetone and phenol of an excess of 8-fold to 15-fold in molar ratio to solid catalysts.
Conventionally, a technique using cation exchange resin or mercapto-modified cation exchange resins as such solid catalysts has been known, and in the mercapto-modified cation exchange resins, the mercaptoalkylamine are partially neutralized and mercapto group is fixed on cation exchange resins.
Concerning solid catalysts other than the ion exchange resin catalysts, additionally, a technique using polyorganosiloxane catalysts with both of a sulfonic acid group-containing hydrocarbon group and a mercapto group-containing hydrocarbon group as solid catalysts is described for example in U.S. Pat. No. 5,631,338, U.S. Pat. No. 5,789,628, EP-A-765,897, and EP-A-856,505. Compared with ion exchange resin catalysts, the polyorganosiloxane catalysts are known to have very high catalytic activity and selectivity.
These polyorganosiloxane catalysts are generally porous substances synthetically produced by so-called sol-gel process comprising hydrolysis of alkoxysilanes of different types and subsequent dehydration-condensation; and the porous substances comprise a macro-porous region of a pore size of 200 angstroms or more and a meso-porous region of a pore size within a range of 20 to 200 angstroms. The mean pore size in the meso-porous region is generally 20 to 100 angstroms. So as to recover high catalytic activity, generally, the specific surface area is 500 to 1500 m.sup.2 /g; and the total amount of the sulfonic acid group-containing hydrocarbon group and the mercapto group-containing hydrocarbon group is generally about 2.5 to 8.5 .mu.mol per unit surface area (1 m.sup.2).
In case that polyorganosiloxane catalysts are used for flow reaction on fixed bed to produce bisphenolA, additionally, it has been known that the catalyst life of the polyorganosiloxane catalysts can be prominently improved by adding a trace amount of water to the starting materials acetone and phenol, as in the case of the use of mercapto-modified cation exchange resin catalysts described in Japanese Patent Laid-open No. 172241/1994 for flow reaction on fixed bed.
However, the serious problem of the polyorganosiloxane catalysts, namely the continuous decrease of the catalytic activity thereof as the reaction time passes even by the addition of water to the raw materials, has not yet been overcome. Thus, the polyorganosiloxane catalysts have not yet been applied industrially.
As described above, the currently known polyorganosiloxane catalysts cannot be applied in practice because the deterioration of the catalysts, namely the continuous decrease of the catalytic activity as the reaction time passes, is serious. When such catalysts are charged as they are on fixed bed, problematically, the frequency of the exchange of the catalyst is increased, involving the elevation of the production cost of the resulting product, which is industrially disadvantageous.
Accordingly, it is a purpose of the invention to provide a catalyst with the deterioration thereof under suppression.